This is especially important for sporting events that run long or shows that air after live sporting events that ran long. But currently when I try to change the current recording via the Android app it creates a 2nd recording. Last night I tried to do this via the web admin UI (since I knew the app wasn't going to work), and it didn't work at all (not even the 2nd recording).
I know you can extend the recording when initially scheduling the recording (which I do for sports and one TV show which airs after sports), but you should be able to do this on the fly as well.
Devices are Android Nvidia Shield and Fire TV.